1. Field of the Invention
The present invention relates to a structure fabrication method for fabricating a structure including a beam structure typified by a comb-structure for use in sensors and actuators to be fabricated by an MEMS technique. “MEMS” is an abbreviation for “micro electro mechanical systems”.
2. Description of the Related Art
In a vertical comb-structure, also called a VC, a pair of comb fingers are arranged to mate with each other, and any one of the comb fingers is supported by an elastic body so as to be out-of-plane deformable.
For fabricating such a structure, using a micro-fabrication technique applied in a semiconductor fabrication method and called the MEMS technique, a micro-structure with a width of one comb-finger of about 5 μm can be fabricated, for example.
Applications of the vertical comb-structure fabricated by the MEMS technique include micromirrors for optical path changing and variable capacitors for radio communication, for example.
A specific example includes the electrodes of electrostatic comb-drive actuators for driving a micro oscillatory structure by an electrostatic force.
In the electrostatic comb-drive actuator using the vertical comb-structure, for displacing the comb-structure from the initial position, the generation of a large drive force is required. For increasing the drive force of a vertical comb-structure, an angular vertical comb structure and its fabrication method have been known (see U.S. Pat. No. 7,089,666). The angular vertical comb structure is also called an AVC.
The AVC and the summary of its fabrication method described in U.S. Pat. No. 7,089,666 are shown in FIGS. 16A to 16C.
The configuration of the AVC described in U.S. Pat. No. 7,089,666 is shown in FIG. 16A.
An AVC 330 includes an oscillating plate 333 journaled on a torsion spring 332 so as to rotate and oscillate about the torsion spring 332 clockwise or counterclockwise and a vertical comb structure 331 arranged on one side of the oscillating plate 333.
The torsion spring 332 is made of a material plastically deformable by being heated, such as silicon and germanium.
A method for inclining the vertical comb structure 331 is shown in FIGS. 16B and 16C.
As shown in FIG. 16B, a pressure back block 335 with a pillar 334 is pushed in straight arrow 338 direction so that the pillar 334 abuts the top surface 337 of the oscillating plate 333 on the opposite side of the vertical comb structure 331, and the oscillating plate 333 is heated.
Thereby, the oscillating plate 333 is rotated in curved arrow 339 direction and the torsion spring 332 plastically deforms in a shape that holds the rotational angle of the oscillating plate 333.
When the vertical comb structure is cooled and the block 335 is removed thereafter, as shown in FIG. 16C, the oscillating plate 333 remains inclined and the vertical comb structure 331 formed on the side of the oscillating plate 333 also maintains the state inclined together with the oscillating plate 333.
For deforming a work piece, it is necessary to apply an external force for applying a moment to generate the rotation of the work piece by some method.
In the fabrication method of the AVC described in U.S. Pat. No. 7,089,666, as shown in FIG. 17, by pushing down the block 335, an external force F is applied to the oscillating plate 333, which is a work piece, and the torsion spring 332 via the pillar 334.
As a result, the component force Fq perpendicular to the oscillating plate 333 of the external force F deforms the oscillating plate 333 and the torsion spring 332 in the rotational direction about the torsion spring 332.
As the deforming angle θ in the rotational direction of the torsion spring 332 is increased, the component force Fq deforming the oscillating plate 333 and the torsion spring 332 in the rotational direction decreases, while the component force Fp that is not contributing to the deformation in the rotational direction increases.
Namely, when the deforming angle θ in the rotational direction of the torsion spring 332 is increased, it is understood that the transmission efficiency of the force decreases during deforming of the oscillating plate 333, which is a work piece, and the torsion spring 332.
Depending on the material, size, and structure of a work piece, the work piece may fall short of the mechanical strength. When such a work piece with insufficient mechanical strength is deformed, unless the force is efficiently transmitted to the work piece, the work piece may buckle or damage during the deforming.